This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2002-240814, filed Aug. 21, 2002; the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a plant and method for producing liquefied natural gas.
2. Description of the Related Art
Recently, liquefied natural gas (LNG) has attracted attention as a clean energy source. LNG is produced in an LNG plant by removing carbon dioxide (CO2) and sulfur components, such as hydrogen sulfide (H2S), from natural gas and removing the moisture content, and then liquefying the resultant gas in a liquefying apparatus. Specifically, CO2 is removed from natural gas so that 50 ppm or less of CO2 remains to prevent generation of dry ice during the LPG production process.
In such an LNG production method, a large amount of combustion exhaust gas containing CO2 is produced by a power source (e.g., boiler) for driving a CO2 recovery apparatus for removing CO2 from natural gas, and a liquefying apparatus. Since CO2 is released into the air as it is, it causes environmental problems including global warming.
The present invention is directed to providing a plant and method for producing liquefied natural gas, which comprises recovering CO2 contained in natural gas and in a combustion exhaust gas generated from a power source, compressing the recovered CO2 by a compressor, feeding out the compressed CO2 from the system by feeding it to a plant such as a urea plant, methanol plant, dimethyl ether plant, or lamp oil/light oil synthesis plant (GTL plant), or the ground, thereby preventing or suppressing emission of CO2 to the air.
According to one aspect of the present invention, there is provided a plant for producing liquefied natural gas comprising:
a carbon dioxide recovery apparatus for natural gas absorbing and removing carbon dioxide from natural gas;
a liquefying apparatus having a steam turbine, for liquefying the natural gas from which carbon dioxide has been removed by the carbon dioxide recovery apparatus;
a boiler equipment for supplying steam to the steam turbine of the liquefying apparatus; and
a carbon dioxide recovery apparatus for combustion exhaust gas including an absorption tower for absorbing carbon dioxide from combustion exhaust gas exhausted from the boiler equipment by absorbing liquid, and a regeneration tower for separating and recovering carbon dioxide from the absorbing liquid.
In the plant for producing liquefied natural gas, it is preferable that the carbon dioxide recovery apparatus for natural gas has an absorption tower for absorbing carbon dioxide from natural gas by absorbing liquid, and a regeneration tower for separating and recovering carbon dioxide from the absorbing liquid and that the regeneration tower also serves as the regeneration tower of the carbon dioxide recovery apparatus for combustion exhaust gas.
According to another aspect of the present invention, there is provided a method for producing liquefied natural gas comprising the steps of:
providing a plant for producing liquefied natural gas comprising:
(a) a carbon dioxide recovery apparatus for natural gas absorbing and removing carbon dioxide from natural gas,
(b) a liquefying apparatus having a steam turbine, for liquefying the natural gas from which carbon dioxide has been removed by the carbon dioxide recovery apparatus,
(c) boiler equipment for supplying steam to the steam turbine of the liquefying apparatus, and
(d) a carbon dioxide recovery apparatus for combustion exhaust gas including an absorption tower for absorbing carbon dioxide from combustion exhaust gas exhausted from the boiler equipment by absorbing liquid, and a regeneration tower for separating and recovering carbon dioxide from the absorbing liquid;
absorbing and removing carbon dioxide of natural gas by the absorbing liquid in the carbon dioxide recovery apparatus for natural gas;
liquefying the natural gas from which carbon dioxide has been removed by the carbon dioxide recovery apparatus for natural gas;
absorbing and removing carbon dioxide of combustion gas exhausted from the boiler equipment by the absorbing liquid in the carbon dioxide recovery apparatus for combustion exhaust gas; and
regenerating the absorbing liquid by separating and recovering carbon dioxide from the absorbing liquid containing carbon dioxide in the regeneration tower of the carbon dioxide recovery apparatus for combustion exhaust gas.
In the method for producing liquefied natural gas, it is preferable that the absorbing liquid containing carbon dioxide absorbed by the carbon dioxide recovery apparatus for natural gas and the absorbing liquid containing carbon dioxide absorbed by the carbon dioxide recovery apparatus for combustion exhaust gas are regenerated by the same regeneration tower.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.